Belt conveyance unit and an image formation apparatus

ABSTRACT

A belt conveyor apparatus and an image formation apparatus therewith are disclosed. The belt conveyor apparatus includes a conveyance belt installed between a driving roller and a follower roller, the conveyance belt being rotationally movable. The position of the conveyance belt in the roller axle direction is regulated by a bead attached to the conveyance belt, and an edge or a slot provided on the driving roller. When the conveyance belt is rotationally moving, the follower roller can move in the thrust direction of the follower roller. The movable amount of the follower roller is made less than the clearance between the bead and the follower roller.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a belt conveyance unit and an image formation apparatus.

2. Description of the Related Art

An ink jet recording device used by image formation apparatuses (such as printers, facsimile apparatuses, reproducing units (copiers), and plotters) forms an image (records) on a recording medium (also called a form, recording paper, imprint paper, etc.) that is conveyed by discharging a drop of recording liquid (for example, ink) from a fine nozzle of a liquid discharging head.

The ink jet recording device, according to Patent References 1, 2, and 3, for example, is configured such that the impact position of an ink drop on the form is precisely configured for high-quality image formation, wherein

a belt conveyance unit, including a conveyance belt, transports a recording medium, the surface of the conveyance belt being uniformly charged so that the recording medium is adhered by the attraction force of the electrostatic charge in order to keep the distance between the recording head and the recording medium constant, and

conveyance of the recording medium is precisely controlled such that the recording medium is correctly positioned without a position gap, is prevented from floating, and is prevented from hitting the recording head causing a jam and liquid smearing.

[Patent reference 1] JPA 4-201469

[Patent reference 2] JPA 9-254460

[Patent reference 3] JPA 2000-25249

As indicated by the above Patent References, the belt conveyance unit includes a conveyance belt that is usually structured by an endless belt, a driving roller, and one or more follower rollers including a tension roller, wherein the conveyance belt is supported by the above-mentioned rollers, and moves around the rollers such that the recording medium is conveyed.

If the conveyance belt, which may be a seamed or seamless belt, supported by at least two rollers, slips in thrust directions of the conveyance belt, conveyance of the recording medium becomes unstable. If this is a conveyance belt of an image formation apparatus, such as especially an ink jet recording apparatus, ink drop impact positions tend to be greatly varied, and a quality image cannot be stably formed.

Then, generally in a mechanism that carries out conveyance with a conveyance belt, which may be seamed or seamless, and at least two or more rollers such as described above, in order to regulate the position in the thrust directions of the conveyance belt, beads that regulate the position and slippage of the conveyance belt are conventionally attached to the inner surface at the circumferential edges of the conveyance belt. Further, one of the rollers, e.g., the driving roller, serves as a slippage standard roller that determines the position of the conveyance belt in the thrust directions. An edge of or a slot formed in the slippage standard roller guides and regulates the bead of the conveyance belt in the directions of the roller axle of the conveyance belt.

Further, as a configuration for regulating wobbling of a conveyance belt by slippage, etc., Patent Reference 4 discloses a technology of detecting wobbling, and selectively dampening both ends of a follower roller in the axle directions of the follower roller; and Patent Reference 5 discloses a technology of detecting wobbling, and changing controlling modes.

[Patent reference 4] JPA, 07-157129

[Patent reference 5] JPA, 10-231041

Furthermore, Patent Reference 6 discloses a conveyance belt wherein warp and woof are arranged such that slippage force is offset.

[Patent reference 6]

Japan Patent No. 3119761

[Problem(s) to be solved by the Invention]

However, according to the structure of such as above Patent References 1, 2, and 3, (wherein the position of the conveyance belt in the roller axle directions is regulated by the bead of the conveyance belt and the end of or the slot formed in the driving roller), although the structure is simple, when the slippage force of the conveyance belt is great, a problem arises in that great reactive force occurs at an interference portion between the beads and the slippage standard roller, and the beads rise, make contact, and are damaged.

Further, one of factors that generate the slippage force of the conveyance belt is torsion between two rollers, which cannot be solved by the conventional structure of such as above Patent References 1, 2, and 3.

That is, while the friction coefficient of the driving roller with reference to the conveyance belt is generally set to be high, a follower roller does not have to generate frictional force as great as the driving roller. When the conveyance belt is supported by two or more axles (rollers), a follower roller, which is arranged just before the driving roller in the belt conveyance direction, serves as a steering roller to steer the conveyance belt should it slip. It is experimentally known that when the conveyance belt slips, the follower roller serving as the steering roller moves in a direction that is opposite to the slippage direction of the conveyance belt. This phenomenon occurs when the follower roller in front of the driving roller (upstream of the conveyance belt movement direction) is in torsion with reference to the driving roller. The conventional structure, without additional measures, cannot rectify the phenomenon.

According to Patent References 4 and 5 above, the slippage is detected by detecting means, and controlling and driving means are required so that controlling and driving are carried out based on detection results of detection means, which complicates the structure. Furthermore, in the case of the technology disclosed by Patent Reference 6, the configuration of the conveyance belt itself is restricted.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to provide a belt conveyance unit, and an image formation apparatus that substantially obviate one or more of the problems caused by the limitations and disadvantages of the related art.

A specific object of the present invention is to provide a belt conveyance unit that can perform stable conveyance, and an image formation apparatus that includes the belt conveyance unit such that a high-quality image can be formed.

Features and advantages of the present invention are set forth in the description that follows, and in part will become apparent from the description and the accompanying drawings, or may be learned by practice of the invention according to the teachings provided in the description. Objects as well as other features and advantages of the present invention will be realized and attained by a belt conveyance unit and an image formation apparatus particularly pointed out in the specification in such full, clear, concise, and exact terms as to enable a person having ordinary skill in the art to practice the invention.

To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides the belt conveyance unit and the image formation apparatus as follows.

The belt conveyance unit according to the present invention regulates the position of the conveyance belt in the roller axle directions by a bead of the conveyance belt, and the end of or a slot formed in the driving roller, wherein, in order to solve the above-mentioned problems, a follower roller, serving as a steering roller, that is arranged just before (upstream of) the driving roller in the belt conveyance direction is provided, the follower roller being movable in the thrust directions of the follower roller while the conveyance belt is moving, the amount of movement of the follower roller in the thrust direction being set less than a clearance between the bead of the conveyance belt and the follower roller.

Here, it is desirable that a roller supporting member for rotatably supporting the follower roller be installed in a direction that reduces torsion between the axle of the driving roller and the axle of the follower roller according to the slippage amount or slippage force of the follower roller. In this case, it is desirable that the structure be such that the slippage force of the follower roller is directly or indirectly transferred to the roller supporting member.

Further, it is desirable that a supporting member for movably supporting the roller supporting member be provided, and that first inclined planes be formed on the supporting member and the roller supporting member that are parallel to each other, but that are not parallel to the directions of the axle of the follower roller such that the roller supporting member is movable in directions perpendicular to the axle directions of the follower roller along the first inclined plane of the supporting member.

In this case, it is desirable that biasing (energizing) means be provided such that the roller supporting member is urged (force is applied) toward the first inclined plane of the supporting member.

Furthermore, a second inclined plane can be provided on the opposite side of the first inclined plane of the roller supporting member. In this case, it is desirable that a contact member be provided on the axle of the follower roller outside of the roller supporting member, the contact member contacting the roller supporting member when the follower roller moves in a direction in which the follower roller is separated from the roller supporting member.

The present invention further provides an image formation apparatus that includes the belt conveyance unit according to the present invention.

EFFECT OF THE INVENTION

According to the belt conveyance unit according to the present invention, the follower roller provided on the upstream side in the belt conveyance direction of the driving roller is movable in the thrust directions of the follower roller while the conveyance belt is rotationally moving. Since the movable distance of the follower roller is set less than a clearance between the bead of the conveyance belt and the follower roller, the follower roller providing a guide function can move in the thrust directions without contacting the bead. In this way, the conveyance belt can provide stable conveyance.

According to the image formation apparatus of the present invention, since the recording medium is conveyed by the belt conveyance unit according to the present invention, the recording medium can be stably conveyed, and a high quality image can be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an example of an image formation apparatus according to the present invention;

FIG. 2 is a plan view of the principal part of the image formation apparatus;

FIG. 3 is a side view showing an outline of a belt conveyance unit according to the present invention;

FIG. 4 is a plan view of an example of the belt conveyance unit;

FIG. 5 is a plan view of another example of the belt conveyance unit;

FIG. 6 is a plan view of the belt conveyance unit for explaining the structure thereof according to the present invention;

FIG. 7 is a side view for explaining a slippage phenomenon of a belt;

FIG. 8 is a plan view for explaining force applied to a follower roller by the belt due to torsion with a conveyance roller;

FIG. 9 is a plan view for explaining force applied to the follower roller due to slippage of the belt;

FIGS. 10A, 10B, and 10C are plan views for explaining the torsion between a driving roller and the follower roller, and slippage directions;

FIGS. 11A, 11B, and 11C are plan views for explaining the torsion between a driving roller and the follower roller, and slippage directions;

FIG. 12 is a cross-sectional view showing the principal part of a belt slippage prevention mechanism according to a first example of the present invention;

FIGS. 13A and 13B show a variation of a bearing of the belt slippage prevention mechanism;

FIG. 14 is a cross-sectional view showing the principal part of a belt slippage prevention mechanism according to a second example of the present invention;

FIG. 15 is a cross-sectional view showing the principal part of a belt slippage prevention mechanism in another operational state according to the second example of the present invention;

FIG. 16 is a cross-sectional view showing the principal part of a belt slippage prevention mechanism according to a third example of the present invention;

FIG. 17 is a cross-sectional view showing the principal part of a belt slippage prevention mechanism in an operational state according to the third example of the present invention;

FIG. 18 is a cross-sectional view showing the principal part of a belt slippage prevention mechanism in another operational state according to the third example of the present invention;

FIG. 19 is a cross-sectional view showing the principal part of a belt slippage prevention mechanism according to a fourth example of the present invention; and

FIG. 20 is a cross-sectional view showing the principal part of a belt slippage prevention mechanism in another operational state according to the fourth example of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention are described with reference to the accompanying drawings. First, an example of the image formation apparatus according to the present invention is described with reference to FIG. 1 and FIG. 2.

The image formation apparatus includes a guide rod 1 and a guide rail 2 that serve as guiding members, and support a carriage 3 free to slide in the direction of main scanning, the guide rod 1 being installed between side plates that are not illustrated. With reference to FIG. 2, the image formation apparatus further includes a main scanning motor 4 that moves the carriage 3 such that scanning is carried out in directions indicated by arrow (the main scanning direction) through a timing belt 5 that is supported by a driving pulley 6 a and a follower pulley 6 b. In addition, guide bushes (bearings) 3 a are arranged in between the carriage 3 and the guide rod 1.

The carriage 3 accommodates a black recording head 7A, and a color recording head 7B. The black recording head 7A includes an ink discharging nozzle for black (Bk) color. The color recording head 7B includes ink discharging nozzles for cyan color (C), magenta color (M), and yellow color (Y). All the nozzles are arranged such that respective inks are discharged downward, i.e., in the direction that is orthogonal to the main scanning direction.

As for energy for the recording heads 7A and 7B to discharge the inks (recording liquid), an actuator is used serving as energy generating means, such as a piezoelectric actuator, a thermal actuator that uses film boiling of a liquid using an electric-thermal conversion element such as an exothermic resistor, a shape memory alloy actuator using the metal phase change due to temperature change, and an electrostatic actuator. Further, the color recording head 7B being capable of discharging three colors may be replaced with three heads, one for each color. Further, colors are not limited to those described above. Furthermore, a two-head configuration may be employed, wherein, e.g., one recording head discharges black and cyan colors, and another recording head discharges magenta and yellow colors.

The carriage 3 includes sub tanks 8 for supplying the inks in each color to the recording heads 7A and 7B. Respective inks are supplied to the sub tanks 8 from respective main tanks (ink cartridges) that are not illustrated through respective ink supply tubes 9. The recording heads 7A and 7B are collectively called the recording head 7.

The image formation apparatus further includes a feed cassette 10, a form loading unit (a pressurizing plate) 11, and a feeding unit. The feeding unit includes a feed roller 13, which is shaped like a half-moon, for carrying form paper 12 sheet by sheet from the form loading unit 11, and a separation pad 14 that is made from a material having a high friction coefficient, and that is arranged countering the feed roller 13. The separation pad 14 is biased toward the feed roller 13.

The image formation apparatus further includes a conveyance unit for conveying the record medium 12 (form) that is fed by the feeding unit to below the recording head 7. The conveyance unit includes a conveyance belt 21 for adhering and conveying the form 12 by electrostatic force, a countering roller 22 for pinching and conveying the form 12 with the conveyance belt 21 wherein the form 12 is provided through a guide 15 from the feeding unit, a conveyance guide 23 for changing the transport direction of the form 12 by about 90° such that the form 12 travels along the conveyance belt 21 approximately perpendicularly, and a tip pressurization roller 25 that is pressed down and biased toward the conveyance belt 21 by a pressurizing member 24. Further, a charging roller 26 serving as electrification means for electrifying the surface of the conveyance belt 21 is provided.

Here, the conveyance belt 21 is an endless belt that can be made endless by molding, or by connecting (seaming) both ends. The conveyance belt 21 is installed between and supported by a conveyance roller 27 that is a driving roller, and a tension roller 28 that is a follower roller. The conveyance belt 21 rotationally moves in a direction called the belt conveyance direction that is the sub-scanning direction as shown in FIG. 2. The rotational movement of the conveyance belt 12 is driven by the conveyance roller 27 rotating through a timing belt 32 and a timing roller 33 driven by a sub-scanning motor 31. In addition, a guide member 29 is arranged on the rear (inner) side of the conveyance belt 21 at a position that corresponds to an image formation area of the recording head 7.

The charging roller 26 contacts an insulation layer (in the case of the belt having a multi-layer structure), which is the surface of the conveyance belt 21 such that the charging roller 26 rotates following the rotational movement of the conveyance belt 21. Force is applied to both ends of the axle of the charging roller 26.

Further, as shown in FIG. 2, a slit disk 34 is attached to the axle of the conveyance roller 27, and a sensor 35 for detecting a slit formed in the slit disk 34 is provided, the slit disk 34 and the sensor 35 constituting an encoder 36.

Further, as shown in FIG. 1, on the front side of the carriage 3, an encoder scale 42 having a slit, and an encoder sensor 43 such as a penetrating type photograph sensor are provided so that the slit of the encoder scale 42 on the front side of the carriage 3 is detected. The encoder scale 42 and the encoder sensor 43 serve as an encoder 44 for detecting a position in the main scanning direction of the carriage 3.

Furthermore, the image formation apparatus includes a delivery unit for delivering the form 12 on which information is recorded by the recording heads 7A and 7B, the delivery unit consisting of a separation nail 51 for separating the form 12 from the conveyance belt 21, a delivery roller 52, a delivery roller 53, and a delivery tray 54 for stacking the form 12 that is delivered.

Further, on the back, a double-side feeding unit 61 is provided, which is attachable and detachable. The double-side feeding unit 61 takes in the form 12 that is returned by rotation in the opposite direction of the conveyance belt 21, turns back the form 12, and feeds the form 12 again between the countering roller 22 and the conveyance belt 21.

Furthermore, a maintenance/recovery unit 71 for maintaining and recovering the state of the nozzles of recording heads 7A and 7B is arranged at one of the non-printing areas in the main scanning directions of the carriage 3. The maintenance/recovery unit 71 includes a suction cap 72 a and a moisturizing cap 72 b for capping the nozzles of the recording heads 7A and 7B. The maintenance/recovery unit 71 further includes a wiper blade 74 for wiping the nozzles of the recording heads 7A and 7B, an off-duty discharging basin 75 for receiving off-duty discharging, etc.

In this manner, according to the image formation apparatus constituted as described above, the form 12 is supplied from the feeding unit sheet by sheet, traveling approximately vertically upward, is guided to the guide 15, is inserted between and conveyed by the conveyance belt 21 and the countering roller 22, is further guided by the conveyance guide 23, is pushed toward the conveyance belt 21 by the tip pressurization roller 25, and is conveyed in the direction approximately horizontal.

At this time, an alternating current voltage is applied to the charging roller 26 such that the conveyance belt 21 is charged with positive bands and negative bands in the sub-scanning direction of the conveyance belt 21, each band having a predetermined width. If the form 12 is fed to the conveyance belt 21 that is alternately charged with the positive and negative bands, the form 12 is adhered to the conveyance belt 21 by electrostatic force, and the form 12 is conveyed by the rotational movement of the conveyance belt 21 in the sub-scanning direction.

Then, by driving the recording heads 7A and 7B according to an image signal, while moving the carriage 3, an ink drop is forced out to the form 12 that is stopped such that a line is recorded. Then, the following line is recorded after moving the form 12 for a predetermined amount of conveyance. By receiving a signal indicating the end of recording, or by the bottom edge of the form 12 arriving at the recording area, the recording operation is ended, and the form 12 is delivered to the delivery tray 54.

In the case of double-side printing, the conveyance belt 21 moves in the opposite direction when the first printing face of the form 12 has been printed, and the form 12 is provided to the double-side feeding unit 61, is reversed (turned back), and is fed between the countering roller 22 and the conveyance belt 21 again such that the reverse side can be printed. Then, the form 12 is conveyed by the conveyance bell 21 by performing timing control, its rear side is printed, and it is delivered to the delivery tray 54.

Further, while standing by for printing (recording), the carriage 3 is moved to the maintenance/recovery unit 71 such that the nozzles of the recording heads 7A and 7B are capped by the suction caps 72 a and the moisturizing cap 72 b for maintaining the nozzles in a wet state such that poor discharging due to ink dryness is prevented from occurring. Further, a recovery operation is carried out wherein recording liquid (ink) is suctioned from the nozzles while the recording heads 7A and the 7B are capped by the suction cap 72 a such that thickened recording liquid and air bubbles are discharged. Further, off-duty discharging is carried out wherein ink that is not currently being used for printing is discharged before a recording start, in the middle of recording, etc. In this manner, discharging performance of the recording heads 7A and 7B is stabilized.

In the following, details of the belt conveyance unit of the image formation apparatus according to the present invention are described with reference to FIG. 3 through FIG. 6. Here, FIG. 3 is a side view showing the outline of the belt conveyance unit, FIG. 4 is a plan view of the belt conveyance unit, FIG. 5 is a plan view of another example of the belt conveyance unit, and FIG. 6 is a plan view of the belt conveyance unit for explaining its structure. Here, different reference numbers are used for variations of members, and the like.

The belt conveyance unit includes a conveyance belt 101, which is looped and endless (corresponding to the conveyance belt 21), installed between and supported by a driving roller 102 (corresponding to the conveyance roller 27), and a tension roller 103 (corresponding to the tension roller 28) that is a follower roller.

In order to rotationally move the conveyance belt 101, a pinion gear 114 fixed to the axle of a sub-scanning motor 113 is engaged with a gear 112 that is fixed to the end section of a roller axle 111 of the driving roller 102. In this manner, the driving roller 102 is rotationally driven by the sub-scanning motor 113 through the gear sequence. In addition, as described above, a structure using a timing belt is possible.

Further, the tension roller 103 is supported free to rotate by roller axles 115 being supported by follower roller bearings 116 that serve as roller supporting members. The tension roller 103 is urged (force is applied) in a direction that increases the distance from the driving roller 102, and tension is given to the conveyance belt 101 by pressurization springs 118 that are installed between the respective follower roller bearings 116 and respective structures (spring supporting units) 117 that are fixing units.

Further, beads 105 for regulating slippage and position of the conveyance belt 101 are provided at both ends (edges) of the inner side of the conveyance belt 101. The beads 105 are fixed to the conveyance belt 101 with an adhesion tape, adhesives, etc. Since the conveyance belt 101 and the beads 105 are united and rotate, the beads 105 need to flexibly follow the movement of the conveyance belt 101. Therefore, it is desirable that the beads 105 be constituted by a flexible material, for example, a urethane system material.

Here, according to the structure shown in FIG. 4, the driving roller 102 has edges 102 a on both its ends that can contact the corresponding beads 105 (one end at a time if the conveyance belt is off-center) such that the position of the conveyance belt 101 in the axle directions is regulated by the beads 105 of the conveyance belt 101 and the edges 102 a of the driving roller 102.

Further, according to the structure shown in FIG. 5, the driving roller 102 has slots 106 on both ends, to which slots 106 the beads 105 are meshed such that the position of the conveyance belt 101 in the axle directions is regulated by the beads 105 of the conveyance belt 101 and the slots 106 of the driving roller 102. In addition, the position of the conveyance belt 101 in the axle directions can be regulated by forming only one slot 106 on one end of the driving roller 102.

Further, a structure wherein three or more rollers are provided for supporting the conveyance belt 101 can be adopted. In this case, a roller that is immediately upstream of the driving roller 102 in the conveyance direction of the conveyance belt 101 serves as the follower roller described by the present invention.

In the belt conveyance unit described here, both ends of the roller axle 115 of the follower roller 103 are supported by corresponding follower roller bearings 116 such that the follower roller (tension roller) 103 can move in the thrust direction of the follower roller 103 while the conveyance belt 101 is rotationally moving.

Further, the belt conveyance unit is structured such that clearances as defined below satisfy certain conditions as follows. Clearances C5 and C6 are between the beads 105 attached to the conveyance belt 101 and the respective edges 102 a of the driving roller 102 as shown in FIG. 6. Clearances C1 and C2 are between the beads 105 of the conveyance belt 101 and the respective edges 103 a of the follower roller 103. Clearances C3 and C4 are between the edges of boss sections 115 a of the roller axles 115 of the follower roller 103 and the respective follower roller bearings 116. The clearances as defined above satisfy both following conditions (1) and (2).

[Equation 1] C1>C4+C5  (1)

[Equation 2] C2>C3+C6  (2)

With the structure as described above, when the conveyance belt 101 becomes off center (slippage occurs), the follower roller 103 moves in the thrust direction that is reverse to the slippage direction of the conveyance belt 101.

In FIG. 6, when the conveyance belt 101 moves in the direction of A indicated by an arrow, the clearance C5 first becomes 0, C5=0. If the formula (I) is satisfied, even if the follower roller 103 moves to the left, a clearance of C1−C5−C4>0 is obtained between the follower roller 103 and the bead 105. Conversely, if the conveyance belt 101 moves in the direction of B indicated by an arrow, a clearance of C2−C3−C6>0 is obtained between the follower roller 103 and the bead 105.

In this manner, the follower roller 103 can move in the direction of the axle until the follower roller contacts the bearing 116 without making contact with the bead 105 attached to the conveyance belt 101.

That is, where the position of the conveyance belt in the roller axle direction is regulated by the bead of the conveyance belt and the edges or slots of the driving roller, the follower roller immediately upstream of the driving roller in the belt conveyance direction is provided such that it can move in the thrust direction of the follower roller while the conveyance belt is rotationally moving, and the movable amount of the follower roller is set at less than a clearance (less than the clearance C3 in the above-mentioned example) between the bead of the conveyance belt and the follower roller. In this manner, the follower roller serving as the steering roller can move in the thrust direction of the conveyance belt without making contact with the bead of the conveyance belt, and the follower roller can move according to the positional relation of torsion with reference to the driving roller; therefore, stable conveyance can be performed.

Next, slippage of the conveyance belt 101 is described. When the belt conveyance unit, being the object of the present invention, is looked at in a line of sight 121 shown in FIG. 7, torsion 122 (torsion angle α) is present between an axle P1 of the driving roller 102 and an axle P2 of the follower roller 103, the torsion being caused by error tolerances of components, the structure, rigidity, and the like as shown in FIG. 8.

If the conveyance belt 101 rotationally moves (and the recording medium is conveyed) while there is such torsion, conveyance force F1 applied to the follower roller 103 by the conveyance belt 101 driven by the driving roller 102 is divided into a component force F2 in the rotation direction of the follower roller, and a component force F3 in the thrust direction of the follower roller at a place where the follower roller 103 contacts the conveyance belt 101 as shown in FIG. 8.

That is, the conveyance belt 101 driven by the driving roller 102 applies the belt conveyance force F1 to the follower roller 103. However, the follower roller 103 is rotating in the same direction as the component force F2 at an angle θ with the conveyance force F1. Accordingly, the force F1 of the belt conveyance is divided into the component forces F2 and F3, causing a gap (twist) to be produced between the follower roller 103 and the conveyance belt 101.

At this time, the follower roller 103 is driven by the conveyance force (moving force) of the conveyance belt 101. The component force F3 (belt slippage force) drives the follower roller 103 in the thrust direction, i.e., in a follower roller slippage direction 126. Slippage force in the slippage direction 126 is labeled F6. Further, since the follower roller 103 is not necessarily supported at a position in the thrust directions without frictional force, reactive force (belt slippage force) F4 is generated against the component force F3, and the reactive force (belt slippage force) F4 causes the conveyance belt 101 to slip in a direction of the belt slippage direction 125 (force in the belt slippage direction 125 is labeled F5).

Here, between the belt slippage force F3 and the slippage force F6, there is an efficiency relation of friction coefficients that are generated between the conveyance belt 101 and the follower roller 103. That is, the slippage force is equal to [(friction coefficient)×F3−(resistance force against movement in the thrust directions of the follower roller 103)]. Further, a relation between the slippage force F5 of the conveyance belt 101 and F4 is such that F5=[(friction coefficient)×(the reaction force F4+resistance force against the movement in the thrust directions of the follower roller 103)].

In this manner, in the case of the state shown in FIG. 8, the conveyance belt 101 is moved in the direction of A indicated by an arrow in FIG. 9, and the follower roller 103 is moved in the direction of B indicated by an arrow. Here, the state of torsion, and the moving directions of the conveyance belt 101 and the follower roller 103 are briefly described with reference to FIGS. 10A, 10B, 10C, 11A, 11B, and 11C.

When the slippage of the conveyance belt 101 is in the direction A indicated by the arrow, and the slippage of the follower roller 103 is in the direction B indicated by the other arrow as shown in FIG. 10A, the left-hand end of the follower roller 103 is offset by an angular torsion amount δ1 with reference to the axle P1 of the driving roller 102 as shown in FIG. 10B. Accordingly, the angle of the follower roller 103 is corrected in the direction of “follower roller angle correction” C shown in FIG. 10C.

Conversely, when the slippage of the conveyance belt 101 is in the direction of B indicated by the arrow, and the slippage of the follower roller 103 is in the direction of A indicated by the other arrow as shown in FIG. 11A, the right-hand end of the follower roller 103 is offset by an angular torsion amount δ2 with reference to the axle P1 of the driving roller 102 as shown in the FIG. 11B. Accordingly, the angle of the follower roller 103 is corrected in the direction of “follow roller angle correction” D shown in FIG. 11C.

Then, the bearing 116, serving as the roller supporting member for supporting the follower roller 103 free to rotate in the slippage direction of the follower roller 103, is structured such that the bearing 116 can move in a direction that reduces the torsion between the axle of the driving roller 102 and the axle of the follower roller 103 according to a slippage amount or slippage force of the follower roller 103. In this manner, the torsion between the driving roller 102 and the follower roller 103 is rectified, and the force F2 is made equal to the force F1 with reference to FIG. 8, nullifying the force F3 and eliminating the slippage of the conveyance belt 101 and the follower roller 103.

That is, if the torsion between the driving roller 102 and the follower roller 103 is rectified, the slippage of the conveyance belt 101 and the movement of the follower roller 103 are also settled. The moving force and amount of the follower roller 103 change with the magnitude of the torsion. The greater is the torsion, the greater is the moving speed of the follower roller 103. Further, the magnitude of the torsion varies from apparatus to apparatus, and for this reason, the amount of the torsion that should be corrected differs from apparatus to apparatus.

The torsion of an individual apparatus is automatically rectified

by the roller supporting member that supports the follower roller free to rotate moving according to a

moving force or an amount of the movement of the follower roller generated by the torsion between the driving roller and the follower roller, and

by automatically adjusting the degree of correction of the supporting position of the supporting member according to the moving situation of the follower roller.

In the following, a “belt slippage stopping mechanism” that makes the bearing 116 movable is described, the bearing 116 serving as the roller supporting member for supporting the follower roller 103 free to rotate.

The first example of the belt slippage stopping mechanism is described with reference to FIG. 12 that is a cross-sectional view for explaining the details of the bearing portion of the follower roller.

Here, a boss section 115 a is formed on the axle 115 of the follower roller 103 in one body, the diameter of the boss section 115 a being greater than the axle 115 and smaller than the follower roller 103. The bearing 116 that serves as the roller supporting member supports the axle 115 of the follower roller 103 free to rotate at a position outside the boss section 115 a.

The undersurface of the bearing 116 is supported by an undersurface supporting section 132 of the structure 117, which serves as the supporting member, such that the bearing 116 is movable in directions E←→F shown by arrows with reference to FIG. 12, i.e., up and down. Here, the undersurface of the bearing 116 is formed as an inclined plane 131 that is not parallel to the axle of the follower roller 103, and an upper surface of the undersurface supporting section 132 of the structure 117 is formed with an inclined plane 133 that is parallel to the inclined plane 131, and not parallel to the axle of the follower roller 103. Here, the inclined plane 133 contacts the inclined plane 131.

As described above, the bearing 116 is supported with its inclined plane 131 being in contact with the inclined plane 133 of the undersurface supporting section (bottom convex) 132, the bearing 116 being able to slide in the directions of the axle of the follower roller 103 on the undersurface supporting section 132. The bearing moves in the directions E←→F as indicated by arrows (E is the direction in which the bearing 116 rises when the bearing 116 moves in a direction pushed by the follower roller in the direction of the axle of the follower roller). Further, the inclined plane 131 of the bearing 116 contacts the inclined plane 133 of the structure 117 free to slide in a direction in which the biasing force provided by the spring 118 mentioned above acts.

Further, on both ends of the bearing 116, guide ribs 135 a, 135 b, 136 a, and 136 b are provided in order to regulate the moving range of the follower roller 103 in the direction of the axle (the thrust direction), the guide ribs being capable of contacting the side of the undersurface supporting section 132 and an upper convex 134 of the structure 117.

In addition, the inclined plane 131 of the bearing 116 can also be formed by a rib 140 installed at both ends in directions that perpendicularly intersect the axle directions as shown in FIGS. 13A and 13B. In this manner, the frictional resistance at the time of sliding is reduced.

Actions of the belt slippage stopping mechanism according to the first example are described. Due to torsion between the driving roller 102 and the follower roller 103, slippage of the conveyance belt 101 and slippage of the follower roller 103 arise. For example, since the formulas (1) and (2) are satisfied as described above, when the follower roller 103 slips in the direction of B indicated by arrow in FIG. 12, the follower roller 103 moves in the direction of B without contacting the bead 105.

Therefore, the edge of the boss section 115 a of the follower roller 103 contacts the bearing 116, and pushes the bearing 116 in the direction of B indicated by the arrow. Since the inclined plane 131 is held by the inclined plane 133 of the undersurface supporting section 132, if the bearing 116 moves in the direction of B indicated by the arrow, the bearing 116 rises in the direction of E in response to force 138 according to the amount of movement. The left-hand side end of the follower roller 103 moves upward in FIG. 12, and the left-hand side position (supporting point that supports free rotation) of the follower roller 103 is changed.

The movement of the bearing 116 becomes greater as the follower roller 103 moves upward in FIG. 12, and continues until the movement stops in the state of FIG. 10C, i.e., until the axle of the driving roller 102 becomes parallel to the axle of the follower roller 103. Consequently, the slippage of the follower roller 103 and the slippage of the conveyance belt 101 are stopped.

Further, when the slippage of the follower roller 103 is in the direction of A indicated by the arrow shown in FIG. 11C, the bearing 16 will descend in the direction of F in FIG. 12, and the slippage of the follower roller 103 and the slippage of the conveyance belt 101 are stopped.

As described above, the structure that moves the supporting position that supports the follower roller free to rotate (the supporting member) is configured such that a part or the whole bottom surface of the supporting member consists of an inclined plane that is not in parallel to the direction of the axle of the follower roller. Further, the inclined plane is parallel to the undersurface supporting section that supports the undersurface of the supporting member. Accordingly, when the supporting member moves in the axle directions of the follower roller, the supporting member moves along the inclination of the undersurface supporting section, and the slippage of the follower roller and the slippage of the conveyance belt are reduced.

That is, when changing inclination of the follower roller in order to rectify torsion between the driving roller and the follower roller of the belt conveyance unit, when the driving roller and the follower roller are arranged approximately horizontal, the position of one or both of the axial ends of the follower roller are moved in an approximately perpendicular direction.

As described above, the vertical position of the bearing of the belt conveyance unit can be automatically adjusted by the simple structure wherein the vertical position of the bearing, serving as the supporting member, is changed by using the motion in the thrust direction of the follower roller.

Next, the second example of the belt slippage prevention mechanism is described with reference to FIG. 14 and FIG. 15, which are cross-sectional views showing the principal part of the same structure in different states.

The belt slippage prevention mechanism according to the present example includes a spring member (elastic member, energizing member) 141 that is infixed between the bearing 116 and the surface of the inner wall of the top part of the structure 117, the top part being the part that does not have the inclined plane 133. The spring member 141 is for urging (applying a force to) the inclined plane 131 of the bearing 116 in a direction that pushes the inclined plane 131 toward the inclined plane 133 of the undersurface supporting section 132 of the structure 117.

Accordingly, when the follower roller 103 moves in the direction of B indicated by the arrow in FIG. 14, the bearing 116 is pushed, and rises in the direction of E in response to the force 138. At this time, biasing by the spring 141 prevents a gap from occurring between the inclined plane 131 of the bearing 116, and the inclined plane 133 of the undersurface supporting section 132 such that a proper amount of correction of the follower roller 103 is obtained.

Further, if the follower roller 103 moves in the direction of A indicated by the arrow in FIG. 15, the boss section 115 a is separated from the bearing 116, and the bearing 116 moves in the direction of A indicated by the arrow in FIG. 15 such that the amount of torsion of the follower roller 103 is reduced as shown in FIG. 11C, because the bearing 116 is pushed downward by force 143 of the spring 141.

That is, while it is indispensable to provide a certain amount of clearance between the bearing 116 (serving as the roller supporting member for supporting the follower roller 103 free to rotate) and the supporting member 117 such that the bearing is movable according to the movement of the follower roller, the clearance works as a gutter when the bearing moves, the gutter causing fluctuation in the amount of compensation for torsion of the follower roller 103 against the driving roller 102, and preventing the attainment of suitable torsion correction.

In view of above, the structure is made such that the force is given for pushing the bearing toward the supporting member, i.e., downward. In this way, sufficient clearance is obtained for the upper part of the bearing such that a smooth movement in a direction approximately perpendicular to the movement of the bearing in the thrust direction is enabled without producing an unnecessary gutter between the inclined plane of the bearing bottom and the inclined plane of the bearing supporting member, thereby maintaining the suitable position.

Next, the third example of the belt slippage prevention mechanism is described with reference to FIG. 16 through FIG. 18, which are cross-sectional views showing the principal part of the same structure in different states.

The structure of the present example includes a spring member (elastic member) 144, such as a pulling spring, that is infixed between the bearing 116 and a lower part of the undersurface supporting section 132 of the structure 117. The spring member 144 applies a force 145 to the bearing 116, and a force 146 in a direction that pushes (urges) the bearing toward the edge of the boss section 115 a of the follower roller 103.

According to this structure, the inclined plane 131 of the bearing 116 is also pushed toward the inclined plane 133 of the undersurface supporting section 132 of the structure 117 by the force 145. Therefore, when the follower roller 103 moves in the direction of B indicated by the arrow shown in FIG. 17, and when the follower roller 103 moves in the direction of A indicated by the arrow shown in FIG. 18, the bearing 116 moves following the movement of the follower roller 103, since the bearing 116 is pushed to maintain contact with the boss section 115 a by the force 146.

Next, the fourth example of the belt slippage prevention mechanism is described with reference to FIG. 19 and FIG. 20, which are cross-sectional diagrams showing the principal part of the same structure in different states. According to the present example, an inclined plane 153 that has an inclination parallel to the inclined plane 131 is formed on the side opposite to the inclined plane 131 of the bearing 116. Further, an inclined plane 151 that follows the inclined plane 153 is formed at a top convex 154 of the structure 117. Furthermore, a contact member 155 (for example, a C-ring, a projection section, etc.) is fixed to the axle 115 of the follower roller 103 outside the bearing 116, the contact member 155 contacting the bearing 116 when the follower roller 103 separates from the bearing 116, i.e., moves in the direction A.

Accordingly, when the follower roller 103 moves in the direction of B indicated by the arrow as shown in FIG. 19, force 163 acts on (pushes) the bearing 116 because the boss section 115 a pushes the bearing 116, and the bearing 116 rises in the direction of E due to force 138 by sliding contact between the inclined plane 131 and the inclined plane 133.

In contrast, when the follower roller 103 moves in the direction of A indicated by the arrow as shown in FIG. 20, since the contact member 155 attached to the axle 115 of the follower roller 103 pushes the bearing 116 with force 164, the bearing 116 moves in the direction of A indicated by the arrow, and due to force 165 descends in the direction of F, so that the axial supporting position of the follower roller 103 is maintained at a proper position.

That is, the belt slippage stopping mechanism of the belt conveyance unit according to the present invention rectifies torsion that is present between the driving roller and the follower roller, and regulates slippage of the belt. Once slippage of the conveyance belt is corrected, there is no force received in the thrust direction, movement in the approximately perpendicular direction stops, and the bearing that supports the follower roller axle that is free to rotate does not move from the position.

However, when the flatness of the place where the image formation apparatus is placed changes, or when a strain arises in the physical structure of the image formation apparatus by movement, etc., torsion between the follower roller and the driving roller may get worse. When such torsion arises, the follower roller starts movement in the thrust direction, and the position of the bearing has to be corrected again.

At this instance, if the direction to correct the torsion is the same as the correction direction before, the position correction is carried out by the follower roller pushing the bearing in the thrust direction further. However, if the correction direction is reverse, the follower roller moves in the direction departing from the bearing. In this case, the bearing moves in the direction that is reverse to the previous movement according to the movement of the follower roller.

Then, a second inclined plane is provided to the surface opposite to a first inclined plane at the position that supports the follower roller free to rotate, the second inclined plane being parallel to the first inclined plane, and the inclined planes at the upper and lower surfaces of the bearing have forces applied. In this manner, the inclined plane provided on the lower side of the bearing follows the movement of the bearing in an approximately reverse-perpendicular direction without being separated.

Further, the contact member 155 is provided. The contact member is provided on the opposite (outboard) side of the position that supports the following roller from the side of the follower roller in the direction of the axle of the follower roller, and is capable of transmitting force when the follower roller is moved in the axle direction where the follower roller is separated from the position that supports the follower roller.

As for the member (bearing) supporting the follower roller, the amount of torsion between the driving roller and the follower roller may change due to a change in the flatness of the installation place of the image formation apparatus, certain shocks, and the like, and the position of the follower roller may change. At that instance, the bearing that has been pushed in the thrust direction no longer has a force applied, and tends to follow the movement of the follower roller in the changed direction; however, the reaction tends to be dull, and may not follow a small movement of the follower roller.

Then, even when the position of the follower roller changes in the thrust direction, the movement of the bearing can be made to follow the movement of the follower roller by providing points of application of force on both sides in the thrust directions with the bearing being at the center (i.e., providing the boss section 115 a and the contact member 155). Here, the boss section 115 a can be replaced with a structure similar to the contact member 155.

Although the examples applied to the image formation apparatus such as an ink jet recording device have been described above, the image formation means is not limited to ink jet recording means.

Further, the present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention.

The present application is based on Japanese Priority Application No. 2004-161699 filed on May 31, 2004 with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference. 

1. A belt conveyance unit including a conveyance belt that is installed between a driving roller and a follower roller such that the conveyance belt is rotationally movable, wherein a position of the conveyance belt in directions of axles of the rollers is regulated by a bead attached to an inner surface of the conveyance belt for regulating slippage and the position of the conveyance belt, and one of a slot in the driving roller that meshes with the bead and an edge of the driving roller, the belt conveyance unit comprising: a follower roller provided on an upstream side with reference to the driving roller in a belt conveyance direction such that the follower roller can move in a thrust direction of the follower roller, while the conveyance belt is rotationally moving; wherein an amount of the movement of the follower roller in the thrust direction is set equal to or less than clearance between the bead of the conveyance belt and the follower roller.
 2. The belt conveyance unit as claimed in claim 1, further comprising: a roller supporting member for supporting the follower roller such that the follower roller can rotationally move; wherein the roller supporting member is installed such that the roller supporting member can move in a direction that reduces torsion between axles of the driving roller and the follower roller according to an amount of one of slippage magnitude and slippage force of the follower roller.
 3. The belt conveyance unit as claimed in claim 2, wherein the belt conveyance unit is structured such that the slippage force of the follower roller is directly or indirectly transmitted to the roller supporting member.
 4. The belt conveyance unit as claimed in claim 2, further comprising: a supporting member that supports the roller supporting member such that the roller supporting member is movable; wherein the roller supporting member and the supporting member have first inclined planes that are mutually parallel, but that are not parallel to the axle directions of the follower roller such that when the roller supporting member moves in the axle directions of the follower roller, the roller supporting member also moves in the direction perpendicular to the axle directions of the follower roller along the first inclined plane of the supporting member.
 5. The belt conveyance unit as claimed in claim 4, further comprising: an energizing member that urges the roller supporting member toward the first inclined plane of the supporting member.
 6. The belt conveyance unit as claimed in claim 4, wherein the roller supporting member has a second inclined plane on a side opposite to the side of the first inclined plane.
 7. The belt conveyance unit as claimed in claim 6, further comprising: a contact member that is attached to the axle of the follower roller outside of the roller supporting member, the contact member contacting the roller supporting member when the follower roller moves in a direction in which the follower roller is separated from the roller supporting member.
 8. An image formation apparatus that forms an image on a recording medium by an image formation unit while conveying the recording medium, comprising: the belt conveyance unit as claimed in claim
 1. 